Attention and effort on this computer program for consultative diagnosis in medicine have been focused during the past year on two areas primarily, (a) the development of the new CADUCEUS program, and (b) the expansion and updating of the medical knowledge base. Prototypic computer programs have been written for the operation of CADUCEUS and have been preliminarily tested. A substantial portion of the medical knowledge base (diseases of the liver and biliary tract) has been reorganized in the CADUCEUS format. The installation of a dedicated VAX computer this summer will allow these programs to be tested critically and then further work can proceed on both elements. The knowledge base in internal medicine has been expanded so that it now includes over 500 diseases and some 3,450 individual manifestations of disease. Many disease entities which were programmed some years ago have been updated. It is gratifying but not unexpected that this expansion and updating have improved the performance of INTERNIST-I. The pediatrics knowledge base has been significantly expanded also. Considerable progress has been made on an anatomy knowledge base for utilization in CADUCEUS. Progress has also been made on the reorganization of the diagnostic program to a form utilizable for educational and testing purposes by medical students and physicians. Future work will proceed along all of these lines with emphasis on the organization and refinement of the CADUCEUS diagnostic program.